Friendship...

Transparency, integrity and love make a healthy friendship
A lot of energy goes into making a friend. Some people make friends more easily than others. Even then, the process of building an acquaintance into a friendship of value is a lot of work. Many would quickly settle for an arms-length arrangement that can never measure up to a healthy friendship. More is needed to transform a casual acquaintance into a healthy friendship.

Marriage is one of those relationships of value. Reality is that some, if not many, marriages are between two friends who don't make it to become best of friends. So, a healthy friendship can defy marriage partners.
It is important to take a good look at what makes a good, healthy friendship.
A friend, a close friend and the best friend
A friend is someone who knows something about you and likes you; a close friend is one who knows a great deal about you and still loves you; and your best friend is one who knows everything there is to know about you and still loves you.
Two things that I believe make a healthy friendship are proximity and love. Proximity denotes the degree to which friends open up to one another. A healthy friendship is one that benefits from mutual interaction, which is steady intercourse.
A relationship, any relationship for that matter can be compared to a flower in the garden. It needs to be watered and constantly tended, and pruning is part of the process of maintaining a healthy relationship. Two key words to consider here are integrity and transparency.
The integrity of a relationship is built on trust and faith in each other. A healthy relationship needs trust. Transparency relates to the extent to which a relationship remains open to criticism and cleaning up by the other party. When a relationship has these it is like an open system that can be sustained over time and through challenges which inevitably assails any relationship.
Love is measured by the degree of acceptance of one another by the parties involved in the relationship. The opposite of love would be indifference. A friendship can not survive where there is indifference. A healthy relationship is supported by the attitude that registers deviations from the norms for that relationship and takes steps to correct them where necessary.

Love covers a host of characteristics required as the nutrients of the flowers of friendship. These include faithfulness, sincerity, care, and protection. A friendship that has these in good measure is a healthy relationship. One that is deficient in one or more is not a healthy relationship. One friend must respect the ideals and values of  the other even if he doesn't believe them. Friends always give complement when something good goes your way but a true friend is the one who dares to criticize you when you do something wrong that is against the values. 
Ultimately, the test of a friendship rests on unconditional care and support through thin and and thick, through cloudy days and rainy days, through joys and pain.